why is it that in some movies a drop of coffee is used to make heart pump again?
If by "pump again" you mean after it has completely stopped, no coffee will not help you.
Your best bet would be some adrenaline injected straight to the heart.
Adrenaline is a hormone produced by the adrenal gland.
When it is produced in the body it stimulates the heart-rate, dilates blood vessels and air passages, and has a number of more minor effects.
Adrenaline is naturally produced in high-stress or physically exhilarating situations.